Tetrafluoroborate Complexes Research Articles

Complexes of a Noncyclic Carbazole-based N5-donor Schiff base: Structures, Redox, EPR and Poor Activity as Hydrogen Evolution Electrocatalysts.

A new noncyclic pentadentate N5-donor Schiff-base ligand, HL2Etpyr (1,1'-(3,6-ditert-butyl-9H-carbazole-1,8-diyl)bis(N-(2-(pyridin-2-yl)ethyl)methanimine)), prepared from 1,8-diformyl-3,6-ditertbutyl-carbazole (HUtBu) and two equivalents of 2-(2-pyridyl)ethylamine, along with four tetrafluoroborate complexes, [MIIL2Etpyr](BF4), where M = Co, Ni, Cu, and Zn, and two [CoIIL2EtPyr]·1/2[CoIIX4] complexes where X = NCS or Cl, isolated as solvates, are reported. All six complexes were structurally characterized, revealing the cations to be isostructural, with M(II) in a trigonal bipyramidal N5-donor environment. Only the Zn(II) complex is fluorescent. Cyclic voltammograms of [MIIL2Etpyr](BF4) in MeCN reveal reversible redox processes at positive potentials: 0.61 (Zn), 0.62 (Cu), 0.57 (Ni), and 0.25 V (Co), and for the cobalt complex a second quasi-reversible process occurs at 0.92 V vs Fc+/Fc. EPR data for the first oxidation product clearly demonstrate that the Zn complex undergoes a ligand centered oxidation, and support this being the case for the Ni and Cu complexes, although this is not definitively shown. After both oxidations the EPR data shows that the Co complex is best described as a low spin Co(III)-ligand radical. In the presence of 80 mM acetic acid, controlled potential electrolysis carried out on [MIIL2Etpyr](BF4) at -1.68 V in MeCN shows some electrocatalytic hydrogen evolution reaction (HER) performance in the order Ni(II) > Cu(II) > Co(II) - but the control, Ni(II) tetrafluoroborate, is more active than all three of the complexes.

Ionic Ruthenium and Iron Based Complexes Bearing Silver Containing Anions as a Potent New Class of Anticancer Agents

A series of salt complexes of the type [RuCl(η6-arene)(κ2-dppm)]+[AgCl(hfac)(PMe3)]−(arene = benzene (1a) or p-cymene (1b), hfac = hexafluoroacetylacetato, dppm = 1,1-bis(diphenylphosphino)methane) have been prepared in a facile route by reaction of [RuCl2(η6-arene)(κ1-dppm)] with [Ag(hfac)(PMe3)]. The iron complex: [CpFe(CO)(κ2-dppm)]+ [AgI(hfac)(PMe3)]− (4) (Cp = η5-C5H5) was also isolated in an analogous fashion by reacting the known complex [CpFeI(CO)(κ1-dppm)] with [Ag(hfac)(PMe3)]. The complexes were fully characterised by spectroscopic means including multinuclear NMR spectroscopy, IR, ESI-MS and UV-Vis. In all cases broad signals are observed in the 31P{1H} NMR spectra corresponding to the P atom in the anion [AgX(hfac)(PMe3)]− (X = Cl or I) which suggests fluxional behaviour. Confirming this picture, the single crystal X-ray diffraction analysis of [CpFe(CO)(κ2-dppm)]+[hfac]− (4-D) is presented, obtained as a decomposition product of compound 4 corresponding with the loss of “AgI(PMe3)”. The nature of the elusive anion [AgX(hfac)(PMe3)]− was investigated by DFT methods (BP86 functional, the ma-def2-SVP basis set for all atoms) showing a weak interaction between the oxygen atoms of the hfac− moiety and the Ag centre. Calculated IR spectra were compared to those obtained experimentally and show an excellent agreement, confirming this picture. The in vitro cytotoxicity on two breast cancer cell-lines (MCF-7 and MDA-MB-231) of all compounds is reported and compared to cisplatin as positive control. The tetrafluoroborate complexes: type [RuCl(η6-arene)(κ2-dppm)]+BF4− (arene = benzene (2a) or p-cymene (2b)) were also prepared and tested in order to elucidate the effect of the silver anion on cytotoxicity and selectivity in 1a and 1b. Moreover, the complex [CpFe(CO)(κ2-dppm)]+BF4− (3) was also prepared for comparison to 4, bearing the silver anion. In general, all complexes exhibit remarkable cytotoxicity and selectivity profiles on both cell-lines, and out-perform cisplatin. The presence of silver in the anion (in compounds 1a, 1b and 4) on average enhance their cytotoxicity compared to their corresponding BF4 analogues. The most active and selective in the entire series is compound 4, which demonstrates that these compounds represent high potential in anticancer applications. Moreover, compounds 4 and 1a inhibited the long-term survival and migration of oestrogen receptor positive (MCF-7) and triple negative (MDA-MB-231) breast cancer cell lines tested respectively. Additionally, compounds 4 and 1a induced morphological and molecular characteristics of apoptosis in MCF-7 and MDA-MB-231 breast cancer cells respectively.

Solvatochromism of Copper(II) Complexes Derived from Trifluoroacetylacetone and Dinitrogen Ligands

Mixed ligand copper(II) complexes of the empirical formula [Cu (L)(TFAA)]X, where L represents 2,2´-bipyridine (Bipy), 1,10´-phenanthroline (Phen), or 4,7-diphenyl-1,10´- phenanthroline (Dphen), TFAA is 1,1,1-Trifluoro-2,4-pentanedione, and X is the counter ion (BF4- or ClO4-), were synthesized and characterized by spectroscopic, magnetic, molar conductance, elemental, and thermal analysis. Solvatochromic studies revealed that all the complexes showed bathochromic shifts. A square planar geometric structure is proposed for the perchlorate and tetrafluoroborate complexes. Spectral properties supported a square planar structure provided by the N2O2 chromophores. The mixed ligand copper complexes exhibited promising catalytic activity in the decomposition of hydrogen peroxide via the first-order reaction; the catalytic efficiency of perchlorate complexes was greater than that of tetrafluoroborate complexes. Potentiometric analyses of the aqueous mixed ligand copper complexes were carried out. The protonation constants of the free ligands and the stability constants of the complexes were determined using pH titration. The sequence of the stability of ternary complexes with respect to their ligands decreased in the order: Bipy˃ Phen˃ Dphen. The kinetic and thermodynamic parameters were calculated using the Coat-Redfern equation. The stability of the complexes was observed to be in line with the results obtained from the potentiometric analyses. The synthesized complexes were examined for their antimicrobial activity against two pathogenic bacteria (Staphylococcus aureus)as Gram-positive bacteria and (Pseudomonas fluorescens) as Gram-negative bacteria and one type of fungus (Fusarium oxysporum). The results indicated that the complexes exhibited higher antimicrobial activity than the ligands. It was also observed that perchlorate complexes had higher activity than tetrafluoroborate, and the growth of inhibitory activity of the complexes followed the order Bipy˃ Phen˃ Dphen.

Mild and Rapid Aniline/HBF4•DEE‐Catalysed Formation of Sulfinyl Imines

AbstractThe combination of anline and tetrafluoroboric acid diethyl etherate (2.5 mol% and 5 mol%, respectively) significantly accelerates the formation of sulfinyl imines in dichloromethane and isopropylacetate at room temperature compared to previous procedures. A DFT and NMR spectroscopic study shows that the anilinium tetrafluoroborate complex is solvated by sulfinamide molecules in the initial state and that the rate‐limiting step of the reaction is the addition of the sulfinamide molecule to the protonated aniline‐based imine. In addition, the catalytic system was also utilised in a one‐pot, two step reaction, where the in situ formed sulfinyl imine was arylated in a rhodium catalysed reaction with high diastereoselectivity.

Iron(ii) tetrafluoroborate complexes of new tetradentate C-scorpionates as catalysts for the oxidative cleavage of trans-stilbene with H2O2.

Attachment of a 2-methylpyridyl group onto the unique 1-nitrogen atom on nitrogen-confused C-scorpionates with either pyrazol-1-yl or 3,5 dimethylpyrazol-1-yl donors gives two new cis-directing tetradentate-N4 ligands (L and L*). The complexes [(L or L*)Fe(CH3CN)2](BF4)2 (1 or 2) were prepared, fully characterized, and investigated for their ability to catalyse the oxidative cleaveage of trans-stilbene in CH3CN. Complexes 1 and 2 are capable of catalysing stilbene cleavage when H2O2 is used as an oxidant but up to six different products are formed, with C[double bond, length as m-dash]C cleavage products (benzaldehyde and benzoic acid) dominating over four products of oxygen transfer. Catalytic amounts of 1 or 2 enhance the ability for the organic photocatalyst riboflavin tetraacetate to use atmospheric oxygen and blue light irradation (450-460 nm) to selectively cleave stilbene to benzaldehyde. However, when benzaldehyde oxidizes further to benzoic acid, the iron species begin giving increasing amounts of stilbene oxygenation products.

Self‐assembly and lower critical solution temperature properties of supramolecular block copolymer/ionic liquid complexes depending on the alkyl chain length of imidazolium rings

ABSTRACTWe report the liquid crystalline (LC) assembly and lower critical solution temperature (LCST) properties of wedge‐shaped block copolymer (BCP)/1‐alkyl‐3‐methylimidazolium tetrafluoroborate ([CnMIM][BF4], n = 2, 4, 6) complexes (1–3) depending on the alkyl chain length of the ionic liquids (ILs). In contrast to the crystalline BCP, all of the ionic samples showed LC phases. 1 with [C2MIM][BF4] exhibited a hexagonal columnar phase, and 3 with [C6MIM][BF4] exhibited a gyroid phase. Interestingly, a temperature‐dependent transformation from columnar phase to gyroid phase was revealed for 2 with [C4MIM][BF4]. The phase difference may be explained by the supramolecular shape change that was dependent on the alkyl chain length of the ILs. The LCST behavior was characterized using the differential scanning calorimetry, turbidity observations, and the X‐ray diffraction techniques. Notably, the primary d‐spacing began to decrease at the clouding temperature (Tc). 3 showed the highest Tc at 130 °C, which is greater than the temperature of the order‐to‐disorder transition. The results demonstrate that the subtle variation in the IL structure affects the morphological and LCST properties. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3587–3596

Inner-Sphere versus Outer-Sphere Coordination of BF4– in a NHC-Gold(I) Complex

The role of counterions in chemistry mediated by gold complexes stretches much further than merely providing charge balance to cationic gold species. Interplay between their basicities and coordination strengths influences interactions with both the gold center and substrates in catalysis. Actual monogold(I) active species are generally believed to be monocoordinated species, formed from the abstraction or the decoordination of a second ligand from precursor complexes, but only a small amount of experimental evidence exists to underpin the existence of these transient species. The formation of a bench-stable neutral IPrCl-gold(I) tetrafluoroborate complex is reported herein. Experimental studies by X-ray diffraction analysis and NMR spectroscopy and theoretical studies by DFT calculations were conducted to determine the composition, structure, and behavior of this complex. The absence of an auxiliary ligand resulted in inner-sphere coordination of the counterion in the solid state. In solution, an equilib...

STOICHIOMETRY AND STRUCTURE OF TETRAFLUOROBORATE COMPLEXES OF Zn(II) WITH ISOMERIC PHENYLENDIAMINES

The tetrafluoroborate complexes of Zn (II) with o-, m- and p-phenylenediamines (FDA) have been synthesized. The investigation of the stoichiometry and the structure of synthesized compounds have been carried out by different physicochemical methods. In accordance with the results of element analysis and atomic absorption spectroscopy the compounds of general formula Zn(FDA)4(BF4)2have been obtained for m- and p-isomers independently of synthesis method. In the case of o-FDA at a synthesis without a solvent and components ratio 1:6 the complex Zn(o-FDA)2(BF4)2 has been synthesized. The lowering of ratio Zn:o-FDA to 1:4 and the ethanol use as a solvent resulted in two water molecules inclusioninto inner coordination sphere [Zn(o-FDA)2(H2O)2](BF4)2.The molar conductivity measurement of dimethylformamide solutions of synthesized compounds shown that complexes are the three-ionic electrolytes of general formula [Zn(FDA)4](BF4)2for m- and p-FDA and [Zn(о-FDA)2](BF4)2 and [Zn(о-FDA)2(H2O)2](BF4)2for o-FDA.The centers of the organic ligand coordination and the outer sphere character of the BF4-bonding have been found by IR spectroscopy. It was determined the nature of the organic ligand and synthesis method determine the stoichiometry and structure of complexes.

Synthesis, characterization and structural elucidation of dicarbonyl(η5-pentamethylcyclopentadienyl)ruthenium(II) complex salts of 1-alkylamines

Five new 1-alkylaminedicarbonyl(η5-pentamethylcyclopentadienyl)ruthenium(II) tetrafluoro-borate complex salts, [Cp*Ru(CO)2NH2(CH2)nCH3]BF4 (Cp*=η5-C5(CH3)5; n=0 (1), 1 (2), 2 (3), 3 (4) and 4 (5)) have been synthesized by the reaction of the Lewis acid [Cp*Ru(CO)2]BF4 with a slight excess of the 1-alkylamines in dry methylene chloride. The water-soluble complexes are reported for the first time and have been characterized by IR, NMR and high resolution mass spectrometry. In aqueous solution, the complexes decompose after 1h. The 1-alkylamines are linked to the ruthenium centre by a sigma bond via the nitrogen atom of the NH2 group. The crystal structure of the complex [Cp*Ru(CO)2NH2CH2CH3]BF4 (2) was obtained by single crystal X-ray diffraction. It crystallizes in the triclinic crystal system, space group P1¯.

Zinc Complexes with Guanidine‐Pyridine Hybrid Ligands: Anion Effect and Catalytic Activity

AbstractThe guanidine‐pyridine ligands DMEGqu, TMGqu, and DMEGpy were reacted with zinc benzoate, zinc acetylacetonate, zinc bromide, zinc tetrafluoroborate, and zinc d,l‐lactate in order obtain the corresponding complexes. The compounds were structurally characterized by X‐ray crystallography and further characterized by NMR, IR, and MS measurements. All complexes were tested as initiators in the melt polymerization of d,l‐lactide and the influence of the anion effect was studied. The bis(chelate) tetrafluoroborate complex 7 exhibited the highest activity.

Simultaneous determination of hydrazine and phenyl hydrazine using 4′-(4-carboxyphenyl)-2,2′:6′,2″ terpyridine diacetonitrile triphenylphosphine ruthenium(II) tetrafluoroborate complex functionalized multiwalled carbon nanotubes modified electrode

A nanocomposite based on the incorporation of the complex 4′-(4-carboxyphenyl)-2,2′:6′,2″ terpyridine triphenylphosphine diacetonitrile ruthenium(II) tetrafluoroborate with multiwalled carbon nanotubes and ionomer supported upon a glassy carbon electrode substrate is reported and characterized with scanning electron microscopy, transmission electron microscopy and infrared spectroscopy. The electrochemical behavior and stability of the composite electrode was investigated via cyclic voltammetry. The modified electrode exhibits an electro-catalytic activity towards the oxidation of both hydrazine and phenyl hydrazine in 0.1M phosphate buffer solution (PBS, pH 7.4). The oxidation of hydrazine and phenyl hydrazine occurs at 0.81V and 0.32V with limit of detection found to be 3.7×10−7M and 1.15×10−7M and having a linear range from 5×10−6M to 6.5×10−3M, and 5×10−6M to 0.2×10−3M, respectively.

Electronically tunable anion-π interactions in pyrylium complexes: experimental and theoretical studies.

Noncovalent interactions of anions with electron-deficient aromatic rings that have been studied so far involve non-heteroaromatic or nitrogen-based heteroaromatic systems. Here we report the first case of an organic oxygenated aromatic system, in particular the tri-aryl-pyrylium tetrafluoroborate system, for which noncovalent anion-π interactions of the pyrylium cation with the tetrafluoroborate anion have been experimentally detected and demonstrated by means of (19)F NMR spectroscopy in solution. A series of pyrylium tetrafluoroborate salts were synthesized in the presence of BF3·Et2O, by direct reaction of 4-substituted benzaldehydes with 4-substituted acetophenones or via the previously obtained chalcone of the less reactive ketone. Correlations of (19)F NMR chemical shifts of tetrafluoroborate anion for most of the synthesized tri-arylpyrylium tetrafluoroborate complexes with both the pyrylium cation molecular weight and the standard substituent Hammett constants, demonstrate anion-π(+) interaction to act between the polyatomic anion BF4(-) and the pyrylium aromatic system. DFT calculations reveal that an additional (C-H)(+)-anion hydrogen bond involving the H(5) of pyrylium ring exists for these fluorescent dyes that show a tunable cup-to-cap shape cavity. The strong fluorescence emission observed for some representative pyrylium tetrafluoroborates described herein, makes them a promising class of tunable emission wavelength dyes for laser technology applications.

Synthesis, characterisation and crystal structures of new water-soluble 1-alkanaminedicarbonyl(η5-cyclopentadienyl)ruthenium(II) tetrafluoroborate complex salts

New water-soluble 1-alkanaminedicarbonyl(η5-cyclopentadienyl)ruthenium(II) tetrafluoroborate complex salts, [CpRu(CO)2NH2R]+BF4− (Cp=η5-C5H5) (R=CH31, C2H52, C3H73, C4H94, C5H115 and C6H136), were synthesised by the reaction of the organometallic Lewis acid, [CpRu(CO)2]+BF4, with slight excesses of 1-alkanamines, RNH2, in dry methylene chloride at room temperature and pressure. These compounds are reported for the first time and have been fully characterised by IR, electrospray ionisation mass spectroscopy, 1H and 13C NMR spectroscopy, and elemental analysis. Spectral data show that the n-alkanamines are σ-bonded to the metal centre via the nitrogen atom. Complexes 2–5 were characterised by single crystal X-ray diffraction and all four cationic species feature a “pseudo-octahedral three-legged piano stool” structure in which the ruthenium centre is coordinated through a sigma bond to the amine N atom and two carbonyl ligands at the base of the stool and the cyclopentadienyl ring in the apex of the stool. IR studies showed that peaks of the νCO stretching vibrations shifted slightly to lower frequency as the carbon chain length increased. The melting point and percentage yields were observed to generally decrease with increase in n-value.

Well-Defined Iron Catalyst for Improved Hydrogenation of Carbon Dioxide and Bicarbonate

The most efficient, stable, and easy-to-synthesize non-noble metal catalyst system for the reduction of CO(2) and bicarbonates is presented. In the presence of the iron(II)-fluoro-tris(2-(diphenylphosphino)phenyl)phosphino]tetrafluoroborate complex 3, the hydrogenation of bicarbonates proceeds in good yields with high catalyst productivity and activity (TON > 7500, TOF > 750). High-pressure NMR studies of the hydrogenation of carbon dioxide demonstrate that the corresponding iron-hydridodihydrogen complex 4 is crucial in the catalytic cycle.

Crystal Structure Analysis of Two Chloro(2,2′:6′,2″-terpyridine)gold(III) Complexes

The X-ray crystal structure analysis of [AuCl(terpy)](BF4)2 and [AuCl(terpy)](SO3CF3)2 show with the counter anions BF4 − and SO3CF3 − an expanded, more or less distorted octahedral coordination geometry. These secondary bonding interactions of the counter anions with the square planar complex cation [AuCl(terpy)]2+ are discussed and compared with those found in related gold(III) terpyridine complexes. In [AuCl(terpy)](SO3CF3)2 a very short non-bonding Au–O distance of 2.7641(4)A of one of the triflate ions was found. The tetrafluoroborate complex is monoclinic with space group P21/c and cell parameters a = 8.7587(12)A, b = 13.2623(19)A, c = 15.537(2)A, β = 90.362(2)°, V = 1804.7(4)A3, Z = 4. The triflate complex is triclinic with space group P $$ {\bar{\text{1}}} $$ and cell parameters a = 7.4198(15)A, b = 12.069(2)A, c = 13.583(3)A, α = 101.414(3)°, β = 101.922(3)°, γ = 94.838(4)°, V = 1156.6(4)A3, Z = 2. The solid state structures of [AuCl(terpy)]X2 (X = BF4, SO3CF3)2 show with the counter anions an expanded, more or less distorted octahedral coordination geometry.

Electro-oxidation of phenyl hydrazine on a modified electrode constructed using nanocomposite of ruthenium terpyridyl complex, multiwalled carbon nanotubes and nafion

A modified glassy carbon electrode has been constructed using a 4′-(4-carboxyphenyl)-2, 2′: 6′, 2′′- terpyridine(1, 10-phenanthroline)chloride ruthenium (II) tetrafluoroborate complex along with multiwalled carbon nanotubes and nafion. The synthesized composite has been characterized using scanning electron microscopy, Transmission electron microscopy, and UV-Visible spectroscopy and IR spectroscopy. Electrochemical behaviour and stability of modified electrode has been investigated by cyclic voltammetry. Electrocatalytic activity of the modified electrode was investigated for the oxidation of phenyl hydrazine in 0.1M phosphate buffer solution of pH 7.4. We observed Ruthenium complex/MWCNTs/ionomer composite has better electrochemistry, electrical properties and firm adhesion of the material with homogeneous dispersion at the electrode surface. The modified electrode showed electro-catalytic response to the oxidation of phenyl hydrazine at the potential of 600mV. The linear range and detection limit for the detection of phenyl hydrazine in the optimum condition was found to be 5×10−6 to 0.2×10−3M and 0.15μM respectively. The modified electrode also exhibited several attractive features such as simple preparation, fast response, good stability and repeatability.

Copper(II) and copper(I) tetrafluoroborate complexes with 4-(3,5-diphenyl-1H-pyrazol-1-yl)-6-(piperidin-1-yl)pyrimidine (L): Synthesis, structures and luminescence

Copper(II) and copper(I) complexes, [CuIIL2(BF4)2]·0.5H2O, [CuIL2](BF4)·2MeCN and [CuIL2](BF4)·H2O, with 4-(3,5-diphenyl-1H-pyrazol-1-yl)-6-(piperidin-1-yl)pyrimidine (L) have been synthesized. The compound [CuIIL2(BF4)2]·0.5H2O was obtained in the M:L=1:1 and 1:2molar ratios in EtOH solutions. It represents an example of a complex containing coordinated BF4− anion. The Cu–F(BF3) distances, 1.964(2) and 2.000(2)Å, are the shortest for copper tetrafluoroborate complexes. The compounds [CuIL2](BF4)·2MeCN and [CuIL2](BF4)·H2O were obtained in the M:L=1:1 and 1:2molar ratios in MeCN solutions. According to X-ray data, the molecules of L in the structures of [CuIIL2(BF4)2]·0.5H2O and [CuIL2](BF4)·2MeCN are coordinated to the copper atoms through N2(pyrazole) and N3(pyrimidine) atoms. The complex [CuIL2](BF4)·2MeCN is unstable in the ambient air and transforms into [CuIL2(BF4)]·H2O. The complex [CuIL2](BF4)·H2O was found to display orange photoluminescence.

Protonation reactions of the oxo complex cis-[Mo2(η5-C5H5)2(O)(μ-PPh2)2(CO)]. Hydroxo and tetrafluoroborate derivatives

The dimolybdenum complex cis-[Mo2Cp2(O)(μ-PPh2)2(CO)] (1) reacted with either [H(OEt2)2](BAr′4), (Ar′=3,5-C6H3(CF3)2), or HBF4·OEt2 to give the corresponding hydroxo derivatives [Mo2Cp2(OH)(μ-PPh2)2(CO)]+, which at room temperature rearrange to the oxohydride isomers [Mo2Cp2(μ-H)(O)(μ-PPh2)2(CO)]+ via a protonation/deprotonation sequence involving the hydride-hydroxo complex [Mo2Cp2(μ-H)(OH)(μ-PPh2)2(CO)]2+ (Cp=η5-C5H5). All these cations were characterized spectroscopically in solution, but none of them could be isolated as a solid material. The reaction of 1 with 2equiv of HBF4·OEt2 eventually led to the formation of the tetrafluoroborate complex [Mo2Cp2(κ2-F2BF2)(μ-PPh2)2(CO)](BF4) (Mo–Mo=2.841(2)Å). The BF4− ligand in the latter complex was easily displaced by nitriles at room temperature to give the corresponding tris(nitrile) derivatives [Mo2Cp2(μ-PPh2)2(CO)(NCR)3](BF4)2 (R=Me, Ph), and by acetylacetone (acac-H), to give the acetylacetonate complex [Mo2Cp2(κ2-acac)(μ-PPh2)2(CO)](BF4) (2.831(2)Å).

Metal-Free and Dicopper(II) Complexes of Schiff Base [2 + 2] Macrocycles Derived from 2,2′-Iminobisbenzaldehyde: Syntheses, Structures, and Electrochemistry

Three new bis-terdentate Schiff base [2 + 2] macrocycles (H(2)L(Et), H(2)L(Pr), and H(2)L(Bu)) have been prepared in high yields by 1:1 condensation of 2,2'-iminobisbenzaldehyde with 1,2-diaminoethane, 1,3-diaminopropane, and 1,4-diaminobutane, respectively. Metalation of these macrocycles yields the corresponding dicopper(II) acetate (1, 2, and 3) and tetrafluoroborate (4, 5, and 6) complexes. The structures of H(2)L(Et), H(2)L(Pr), H(2)L(Bu), [Cu(II)(2)L(i)(OAc)(2)]·solvents (where i is Et, Pr or Bu) and [Cu(II)(2)L(Pr)(DMF)(4)] (BF(4))(2)·0.5H(2)O are reported. Intramolecular hydrogen bonding is a feature of the metal-free macrocycles. The copper(II) centers in [Cu(II)(2)L(i)(OAc)(2)]·solvents are four coordinate, and the macrocycles have U-shaped (Et, Bu) or stepped (Pr) conformations. Complex 5 crystallizes with two dimethylformamide (DMF) molecules bound per five coordinate copper(II) center. Electrochemical studies revealed ligand based oxidations for all of the macrocycles and complexes. Complexes 1 and 2 undergo two quasi-reversible oxidations in DCM which are associated with the deposition of a visible film on the electrode after multiple scans in this oxidative region, suggestive of electropolymerization. Complexes 4-6, studied in MeCN, have Cu(II) → Cu(I) redox potentials at more positive potentials than for 1-3.

Manipulating Self-Assembly in Silver(I) Complexes of 1,3-Di-N-pyrazolylorganyls

A series of ligands with two pyrazolyls (pz) linked by either a propyl (pz(2)prop), a benzyl (pz(2)Bn or pzBnpz*, where Bn = benzyl and pz* = 3,5-dimethylpyrazolyl), or a 1,8-naphthyl (pz(2)naphth) spacer and their silver(I) tetrafluoroborate complexes have been prepared with the intent of evaluating how the conformational flexibility of the ligands would affect the supramolecular assembly of the 1:1 [Ag(ligand)](BF(4)) complexes and their capacity for promoting short Ag...Ag interactions. The noncoordinating nature of the tetrafluoroborate anion ensured low coordination numbers to the silver(I) centers, thereby allowing the metal ion to participate in multiple noncovalent interactions that dictate the ligand conformations and supramolecular isomerism observed in the solid state. In the solid state, the complex [Ag(CH(3)CN)(pz(2)prop)](BF(4)) forms a cyclic bimetallic cation that assembles into one-dimensional chains as a result of Ag-pi and CH...F noncovalent interactions, in a manner distinct from the known nitrate derivative. With [Ag(pz(2)Bn)](BF(4)), either cyclic bimetallic cations or coordination polymers can be formed depending on the solvents used for crystallization, where acetone promotes the formation of the former while acetonitrile gives the latter. The complex [Ag(pzBnpz*)](BF(4)) forms two different one-dimensional coordination polymers in the same flask during crystallization from acetone/Et(2)O, where the presence or absence of the included solvent dictates the differences in the secondary coordination sphere of (and noncovalent interactions involving) silver(I). In all the above cases, neighboring silver atoms are separated beyond van der Waals contact. In contrast, the complex [Ag(pz(2)naphth)](BF(4)) x 2 CH(3)CN forms discrete cyclic bimetallic cations where the rigid ligand enforces a short (3.19 A) Ag...Ag contact. All complexes are extensively dissociated in a CH(3)CN solution, as indicated from a combination of (1)H NMR and positive-ion electrospray ionization mass spectral data.